Substituted tolyl esters of 16-substituted-PGE2 -type compounds

ABSTRACT

Substituted phenyl and naphthyl esters of PGE 2  analogs, including the 16-alkyl, 16-fluoro, 16-phenoxy, and phenyl-substituted analogs, and their 15-epimers, and their racemic forms, and processes for producing them are disclosed. The products are useful for the same pharmacological and medical purposes as these PGE 2  analogs, and are also useful as a means for obtaining highly purified 16,16-dimethyl-PGE 2 , 16-phenoxy-17,18,19,20-tetranor-PGE 2 , and 17-phenyl-18,19,20-trinor-PGE 2 .

This is a division of application Ser. No. 523,568, filed Nov. 14, 1974, pending.

BACKGROUND OF THE INVENTION

This invention relates to novel ester derivatives of prostaglandin E₂ analogs (hereinafter identified as "PGE₂ "analogs), including the 16-alkyl, 16-fluoro, 16-phenoxy, and phenyl-substituted analogs, and their 15-epimers, and their racemic forms, and to processes for producing them.

PGE₂ is represented by the formula: ##STR1## A systematic name for PGE₂ is 7-{ 3α-hydroxy-2β-[(3S)-3-hydroxy-trans-1-octenyl]-5-oxo-1α-cyclopentyl]}-cis-5-heptenoic acid. PGE₂ is known to be useful for a variety of pharmacological and medical purposes, for example labor induction and abortion in pregnant animals, including humans, menstrual regulation in both pregnant and non-pregnant animals, including humans, reduction and control of gastric secretion, and as a hypotensive agent to reduce blood pressure in mammals, including humans. See Bergstrom et al., Pharmacol. Rev. 20, 1 (1968) and references cited therein. As to racemic PGE₂, see for example W. F. Schneider, Chem. Commun. 304 (1969).

The 16-alkyl and 16-fluoro analogs of PGE₂ and their 15-epimers are represented by the formula: ##STR2## wherein Y is ##STR3## following the usual convention wherein broken line attachment of hydroxy to the side chain at carbon 15 indicates the natural or "α" configuration and solid line attachment of hydroxy indicates the epi or "β" configuration. In certain instances the "S" and "R" nomenclature are used. See Nugteren et al., Nature 212, 38 (1966) and Cahn, J. Chem. Ed. 41, 116 (1964).

In formula II C_(g) H_(2g) is alkylene of one to 9 carbon atoms, inclusive, with one to 5 carbon atoms, inclusive, in the chain between --CR₁ R₂ -- and terminal methyl; and R₁ and R₂ are hydrogen, methyl, ethyl, or fluoro, being the same or different, with the proviso that at least one of R₁ and R₂ is other than hydrogen, and with the further proviso that R₂ is fluoro only when R₁ is hydrogen or fluoro.

The 16-alkyl and 16-fluoro analogs of PGE₂ and their 15-epimers in their optically active and racemic forms are known. See for example South African Pat. No. 72/1936, Derwent Farmdoc No. 71483T; and South African Pat. No. 73/2244, Derwent Farmdoc No. 69717U. These analogs are also useful for the above-described pharmacological purposes.

The 16-phenoxy and phenyl-substituted analogs of PGE₂ and their 15-epimers are represented by the formula: ##STR4##

In formula III, R₃ and R₄ are hydrogen, methyl, or ethyl; T is alkyl of one to 4 carbon atoms, inclusive, fluoro, chloro, trifluoromethyl, or --OR₅ ; wherein R₅ is hydrogen or alkyl of one to 4 carbon atoms, inclusive, and s is zero, one, 2, or 3, with the proviso that not more than two T's are other than alkyl; Y is ##STR5## and Z represents an oxa atom (--O--) or C_(j) H_(2j), wherein C_(j) H_(2j) is a valence bond or alkylene of one to 9 carbon atoms, inclusive, substituted with zero, one, or 2 fluoro, with one to 6 carbon atoms, inclusive, between --CR₃ R₄ -- and the ring.

The 16 -phenoxy and phenyl-substituted analogs of PGE₂ and their 15-epimers in their optically active and racemic forms are known. See for example South African Pat. No. 73/2818, Derwent Farmdoc No. 73299U; and British Specification No. 1,324,737, Derwent Farmdoc No. 31279J.

Esters of the above compounds are known, wherein the hydrogen atom of the carboxyl group is replaced by a hydrocarbyl or substituted hydrocarbyl group. Among these are the methyl ester of 16-methyl-PGE₂, the methyl ester of 16,16-dimethyl-PGE₂ (A. Robert et al., Gastroenterology 64, 790 (1973)); the phenyl and alkyl-phenyl esters of 16-fluoro- and 16,16-difluoro-PGE₂ (South African Pat. No. 73/2244); the phenyl and alkyl-phenyl esters of 16-phenoxy-PGE₂ (South African Pat. No. 73/2818); and the phenyl and alkyl-phenyl esters of phenyl-substituted PGE₂ (British Specification No. 1,324,737).

SUMMARY OF THE INVENTION

It is a purpose of this invention to provide novel ester derivatives of prostaglandin E₂ analogs, including certain 16-alkyl, 16-fluoro, 16-phenoxy, and phenyl-substituted analogs, their 15-epimers, and their racemic forms. It is a further purpose to provide such esters derived from substituted phenols and naphthols. It is a further purpose to provide such esters in a free-flowing crystalline form. It is still a further purpose to provide novel processes for preparing these esters.

The presently described esters include compounds represented by the generic formula: ##STR6## wherein Y is ##STR7## and wherein R₁₀ is either ##STR8## wherein C_(g) H_(2g) is alkylene of one to 9 carbon atoms, inclusive, with one to 5 carbon atoms, inclusive in the chain between --CR₁ R₂ -- and terminal methyl; and R₁ and R₂ are hydrogen, methyl, ethyl, or fluoro, being the same or different, with the proviso that at least one of R₁ and R₂ is other than hydrogen, and with the further proviso that R₂ is fluoro only when R₁ is hydrogen or fluoro; or ##STR9## wherein R₃ and R₄ are hydrogen, methyl, or ethyl; T is alkyl of one to 4 carbon atoms, inclusive, fluoro, chloro, trifluoromethyl, or --OR₅, wherein R₅ is hydrogen or alkyl of one to 4 carbon atoms, inclusive, and s is zero, one, 2, or 3, with the proviso that not more than two T's are other than alkyl; Z represents an oxa atom (--O--) or C_(j) H_(2j), wherein C_(j) H_(2j) is a valence bond or alkylene of one to 9 carbon atoms, inclusive, substituted with zero, one, or 2 fluoro, with one to 6 carbon atoms, inclusive, between --CR₃ R₄ -- and the ring. In formula IV, E is a substituted phenyl or naphthyl group identified as follows: ##STR10##

    ______________________________________                                         C##STR11##                                                                     D##STR12##                                                                     E##STR13##                                                                     F##STR14##                                                                     G##STR15##                                                                     H##STR16##                                                                     I##STR17##                                                                     J##STR18##                                                                     K##STR19##                                                                     K'#STR20##                                                                     L##STR21##                                                                     M##STR22##                                                                     N##STR23##                                                                     O##STR24##                                                                     P##STR25##                                                                     Q##STR26##                                                                     R##STR27##                                                                     S##STR28##                                                                      ##STR29##                                                                     ______________________________________                                                                        T                                          

For example, the p-acetamidophenyl ester of 16,16-dimethyl-PGE₂ is represented by formula IV when R₁₀ is ##STR30## Y is ##STR31## and E is A, i.e. ##STR32## and is conveniently identified herein as the 16,16-dimethyl-PGE₂ ester of formula IV-A. Racemic compounds are designated by the prefix "racemic" or "dl"; when that prefix ia absent, the intent is to designate an optically active compound.

The novel formula-IV compounds and corresponding racemic compounds of this invention are each useful for the same purposes as described above for PGE₂ and are used for those purposes in the same manner known in the art, including oral, sublingual, buccal, rectal, intravaginal, intrauterine, or topical administration.

For many applications these novel prostaglandin esters which I have obtained from certain specified phenols and naphthols have advantages over the corresponding known prostaglandin compounds. Thus, these substituted phenyl and naphthyl esters are surprisingly stable compounds having outstanding shelf-like and thermal stability. In contrast to the acid form of these prostaglandins, these esters are less subject to acid-catalyzed decomposition either by elimination of water or by epimerization. Thus these compounds have improved stability either in solid, liquid, or solution form. In oral administration these esters have shown surprisingly greater efficacy than the corresponding free acids or lower alkyl esters, whether because of longer duration of biological activity or because of improved lipophilicity and absorption is not certain. These esters offer a further advantage in that they have low solubility in water and the body fluids and are therefore retained longer at the site of administration.

A particularly outstanding advantage of many of these substituted phenyl and naphthyl esters is that they are obtained in free-flowing crystalline form, generally of moderately high melting point, in the range 60°-130° C. This form is especially desirable for ease of handling, administering, and purifying. These crystals are highly stable, for example showing practically no decomposition at accelerated storage tests at 65° C., in comparison with liquid alkyl esters or the free acids. This quality is advantageous because the compound does not lose its potency and does not become contaminated with decomposition products.

These crystalline esters also provide a means of purifying these PGE₂ analogs, particularly 16,16-dimethyl-PGE₂, 16,16-difluoro-PGE₂, 16-phenoxy-17,18,19,20-tetranor-PGE₂, and 17-phenyl-18,19,20-trinor-PGE₂, which are first converted to one of these esters, recrystallized until pure, and then recovered as the free acid. One method of recovering the free acid is by enzymatic hydrolysis of the ester, for example with a lipase. See German Patent 2242792, Derwent Farmdoc No. 23047U.

To obtain the optimum combination of stability, duration of biological activity, lipophilicity, solubility, and crystallinity, certain compounds within the scope of formula III are preferred.

One preference is that E is limited to ##STR33## wherein R₆ is

    ______________________________________                                         CH.sub.3                                                                        ##STR34##                                                                      ##STR35##                                                                     NH.sub.2 ;                                                                     (2)STR37##                                                                      ##STR38##                                                                     ______________________________________                                                                       (3)                                         

wherein R₇ is ##STR39##

Another preference is that E is limited to ##STR40##

Another preference is that E is limited to ##STR41## wherein R₈ is ##STR42## or ##STR43## wherein R₉ is ##STR44##

Especially preferred are those compounds which are in free-flowing crystalline form, for example:

p-benzamidophenyl ester of 16,16-dimethyl-PGE₂

p-(p-acetamidobenzamido)phenyl ester of 16,16-dimethyl-PGE₂

α-semi-carbazono-p-tolyl ester of 16,16-dimethyl-PGE₂

p-acetylphenyl ester of 16-phenoxy-17,18,19,20-tetranor-PGE₂

p-acetylphenyl ester of 17-phenyl-18,19,20-trinor-PGE₂

The substituted phenyl and naphthyl esters of PGE₂ analogs encompassed by formula-IV wherein E is defined by ester groups A through T are produced by the reactions and procedures described and exemplified hereinafter. For convenience, the above prostaglandin or prostaglandin analog is referred to as "the PG compound". The term "phenol" is used in a generic sense, including both phenols and naphthols.

Various methods are available for preparing these esters, differing as to yield and purity of product. Thus, by one method, the PG compound is converted to a tertiary amine salt, reacted with pivaloyl halide to give the mixed acid anhydride and then reacted with the phenol. Alternately, instead of pivaloyl halide, an alkyl or phenylsulfonyl halide is used, such as p-toluenesulfonyl chloride. See for example Belgian patents 775,106 and 776,294, Derwent Farmdoc Nos. 33705T and 39011T.

Still another method is by the use of the coupling reagent, dicyclohexylcarbodiimide. See Fieser et al., "Reagents for Organic Synthesis", pp. 231-236, John Wiley and Sons, Inc., New York (1967). The PG compound is contacted with one to ten molar equivalents of the phenol in the presence of 2-10 molar equivalents of dicyclohexylcarbodiimide in pyridine as a solvent.

The preferred novel process for the preparation of these esters, however, comprises the steps (1) forming a mixed anhydride with the PG compound and isobutylchloroformate in the presence of a tertiary amine and (2) reacting the anhydride with an appropriate phenol or naphthol.

The mixed anhydride is represented by the formula: ##STR45## for the optically active PG compounds, R₁₀ and Y having the same definition as above.

The anhydride is formed readily at temperatures in the range -40° to +60° C., preferably at -10° to +10° C. so that the rate is reasonably fast and yet side reactions are minimized. The isobutylchloroformate reagent is preferably used in excess, for example 1.2 molar equivalents up to 4.0 per mole of the PG compound. The reaction is preferably done in a solvent and for this purpose acetone is preferred, although other relatively non-polar solvents are used such as acetonitrile, dichloromethane, and chloroform. The reaction is run in the presence of a tertiary amine, for example triethylamine, and the co-formed amine hydrochloride usually crystallizes out, but need not be removed for the next step.

The anhydride is usually not isolated but is reacted directly in solution with the phenol, preferably in the presence of a tertiary amine such as pyridine.

The phenol is preferably used in equivalent amounds or in excess to insure that all of the mixed anhydride is converted to ester. Excess phenol is separated from the product by methods described herein or known in the art, for example by crystallization. The tertiary amine is not only a basic catalyst for the esterification but also a convenient solvent. Other examples of tertiary amines useful for this purpose include N-methylmorpholine, triethylamine, diisopropylethylamine, and dimethylaniline. 2-Methylpyridine and quinoline result in a slow reaction. A highly hindered amine such as 2,6-lutidine is not useful because of the slowness of the reaction.

The reaction with the anhydride proceeds smoothly at room temperature (about 20° to 30° C.) and can be followed in the conventional manner with thin layer chromatography (TLC), usually being found complete within 1- 4 hours.

The reaction mixture is worked up to yield the ester following methods known in the art, and the product is purified, for example by silica gel chromatography.

Solid esters are converted to a free-flowing crystalline form on crystallization from a variety of solvents, including ethyl acetate, tetrahydrofuran, methanol, and acetone, by cooling or evaporating a saturated solution of the ester in the solvent or by adding a miscible non-solvent such as diethyl ether, hexane, or water. The crystals are then collected by conventional techniques, e.g. filtration or centrifugation, washed with a small amount of solvent, and dried under reduced pressure. They may also be dried in a current of warm nitrogen or argon, or by warming to about 60° C. Although the crystals are normally pure enough for many applications, they may be recrystallized by the same general techniques to achieve improved purity after each recrystallization.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention can be more fully understood by the following examples.

All temperatures are in degrees centigrade.

Silica gel chromatography, as used herein, is understood to include chromatography on a column packed with silica gel, elution, collection of fractions, and combination of those fractions shown by thin layer chromatography (TLC) to contain the desired product free of starting material and impurities.

"TLC", herein, refers to thin layer chromatography.

Preparation 1 p-Benzamidophenol

A solution of p-hydroxyaniline (20 g.) in 200 ml. of pyridine is treated with benzoic anhydride (20 g.). After 4 hr. at about 25° C., the mixture is concentrated under reduced pressure and the residue is taken up in 200 ml. of hot methanol and reprecipitated with 300 ml. of water. The product is recrystallized frm hot acetonitrile as white crystals, 8.5 g., m.p. 218.0°-218.5° C.

Preparation 2 p-(p-Acetamidobenzamido)phenol

A solution of p-acetamidobenzoic acid (12.5 g.) in 250 ml. of tetrahydrofuran is treated with triethylamine (11.1 ml.). The mixture is then treated with isobutylchloroformate (10.4 ml.) and, after 5 min. at about 25° C., with p-aminophenol (13.3 g.) in 80 ml. of dry pyridine. After 40 min. the crude product is obtained by addition of 2 liters of water. The product is recrystallized from 500 ml. of hot methanol by dilution with 300 ml. of water as white crystals, 5.9 g., m.p. 275.0°-277.0° C.

EXAMPLE 1 p-Benzamidophenyl Ester of 16,16-Dimethyl-PGE₂ (Formula IV-B).

A solution of 16,16-dimethyl-PGE₂ (Belgian Pat. No. 781978, Derwent Farmdoc No. 75254T) (0.095 g.) and triethylamine (0.055 g.) in 10 ml. of acetone is treated at -10° C. with isobutylchloroformate (0.068 g.) with stirring. After about 10 min. the mixture is treated with p-benzamidophenol (Prep. 1, 0.600 g.) in 6 ml. of pyridine for at last one hour at about 25° C. The solvent is removed under reduced pressure. The crude residue is taken up in 100 ml. of chloroform, washed with 75 ml. of 0.1N aqueous monosodium orthophosphate, dried, and concentrated. The residue is subjected to silica gel chromatography, eluting with ethyl acetate-chloroform (1:1). The title compound obtained by concentration of selected fractions, a gummy solid, 0.05 g., is crystallized from ethyl acetate-hexane as white free-flowing crystals, m.p. 62.3°-64.5° C.

R_(f) 0.3 (TLC on silica gel plates in ethyl acetate-acetic acid (97:3)).

EXAMPLE 2 p-(p-Acetamidobenzamido)phenyl Ester of 16,16-Dimethyl-PGE₂ (Formula IV-C)

Following the procedure of Example 1, but using 0.095 g. of 16,16-dimethyl-PGE₂, 0.051 g. of triethylamine, 0.068 g. of isobutylchloroformate, and 0.473 g. of p-(p-acetamidobenzamido) phenol (Prep. 2), there is obtained a crude residue. This residue is dissolved in 50 ml. of dimethylformamide and partitioned between 150 ml. of pH 5.5 Mcllvaine buffer and 200 ml. of ethyl acetate. The organic layer is dried over sodium sulfate and concentrated. The residue, in 8 ml. of ethyl acetate and 1 ml. of dimethylformamide, is subjected to silica gel chromatography, eluting with ethyl acetate-methanol (97:3) and, subsequently, (92:8). The residue obtained by concentration of selected fractions is the title compound, 0.50 g., and is crystallized from methanol-acetone as white free-flowing crystals, m.p. 126°-128° C., R_(f) 0.35 (TLC on silica gel plates in ethyl acetate-acetic acid (97:3)).

EXAMPLE 3 α-Semicarbazono-p-tolyl Ester of 16,16-Di-methyl-PGE₂ (Formula IV-J)

Following the procedure of Example 1, but using 0.095 g. of 16,16-dimethyl-PGE₂, 0.051 g. of triethylamine, 0.068 g. of isobutylchloroformate, and 0.132 g. of p-hydroxybenzaldehyde semicarbazone, there is obtained a crude residue which is taken up in acetonitrile, filtered, and concentrated to a residue. This residue is subjected to silica gel chromatography, eluting with acetonitrile followed by tetrahydrofuran-acetonitrile (3:2). The residue obtained by concentration of selected fractions, 0.06 g., is crystallized from ethyl acetate-hexane as the title compound, white free-flowing crystals, m.p. 84.2°-86.8° C., R_(f) 0.35 (TLC on silica gel plates in ethyl acetate-acetic acid (97:3)).

EXAMPLE 4 p-Acetylphenyl Ester of 16-Phenoxy-17,18,19,20-tetranor-PGE₂ (Formula IV-K)

Following the procedure of Example 1 but using 0.050 g. of 16-phenoxy-17,18,19,20-tetranor-PGE₂ (South African Pat. No. 73/2818, Derwent Farmdoc. No. 73279U), 0.021 ml. of triethylamine, 0.020 ml. of isobutylchloroformate, and 0.0294 g. of p-hydroxyacetophenone, the reaction mixture is further treated as follows. The mixture is diluted with 20 ml. of ethyl acetate and shaken successively with 0.5 N citric acid and 0.2 N phosphate buffer (pH 7.2). The organic phase is dried over sodium sulfate and concentrated. The residue is subjected to silica gel chromatography, eluting with dichloromethane-acetonitrile-methanol (50:50:1). The residue obtained by concentration of selected fractions is crystallized from ethyl acetate-hexane as the title compound, 0.021 g., m.p. 122.6°-124.2° C., R_(f) 0.8 (TLC on silica gel in dichloromethane-acetonitrile (3:2)).

EXAMPLE 5 p-Acetylphenyl Ester of 17-Phenyl-18,19,20-trinor-PGE₂ (Formula IV-K).

Following the procedure of Example 1, but using 0.200 g. of 17-phenyl-18,19,20-trinor-PGE₂, (Great Britain Specification No. 1,324,737, Derwent Farmdoc No. 31279T), 0.089 ml. of triethylamine, 0.0845 ml. of isobutylchloroformate, and 0.109 g. of p-hydroxyacetophenone, the reaction mixture is further treated as follows. It is diluted to 100 ml. with ethyl acetate and shaken successively with 5% aqueous citric acid and phosphate buffer (pH 7.0). The organic phase is dried over sodium sulfate and concentrated. The oily residue is subjected to silica gel chromatography, eluting with ethyl acetate containing 2.3% water. The residue obtained by concentration of selected fractions is crystallized from ethyl acetate-hexane as the title compound, 0.153 g., m.p. 91.7°-92.7° C., R_(f) 0.4 (TLC on silica gel in ethyl acetate-water (98:2)).

Following the procedures of Examples 1-5 but employing the racemic forms of the PG compounds, there are obtained the corresponding esters of racemic PG compounds.

EXAMPLES 6-80

The substituted phenyl and naphthyl esters of 16,16-dimethyl-PGE₂, 16,16-difluoro-PGE₂, 16-phenoxy-17,18,19,20-tetranor-PGE₂, and 17-phenyl-18,19,20-trinor-PGE₂ of Tables I-IV below are obtained following the procedures of Example 1, wherein the prostaglandin compound is reacted in the presence of triethylamine and isobutylchloroformate with the appropriate hydroxy phenyl or naphthyl compound, listed in the Table. These phenols or naphthols are readily available or prepared by methods described herein or known in the art. The crude products, obtained by concentration under reduced pressure, are purified by means described herein or known in the art, including partitioning, solvent extraction, washing, silica gel chromatography, trituration, or crystallization.

Following the procedures of Examples 6-80 but employing the racemic forms of the PG compounds, there are obtained the corresponding esters of the racemic PG compounds.

                  TABLE 1                                                          ______________________________________                                         Esters of 16,16-Dimethyl-PGE.sub.2                                                  Hydroxy Phenyl or   Product 16,16-Dimethyl-                               Ex.  Naphthyl Compound   PGE.sub.2 ester of formula:                           ______________________________________                                          6   p-acetamidophenol   IV-A                                                   7   p-(p-benzamidobenzamido)phenol                                                                     IV-D                                                   8   p-hydroxyphenylurea IV-E                                                   9   p-phenylphenol      IV-F                                                  10   p-tritylphenol      IV-G                                                  11   N-acetyltyrosinamide                                                                               IV-H                                                  12   N-benzoyltyrosinamide                                                                              IV-I                                                  13   p-hydroxyacetophenone                                                                              IV-K                                                  14   p-hydroxybenzamide  IV-L                                                  15   N-(p-tritylphenyl)-p-                                                                              IV-M                                                       hydroxybenzamide                                                          16   p-hydroxybenzoic acid,                                                                             IV-N                                                       methyl ester                                                              17   hydroquinone benzoate                                                                              IV-O                                                  18   hydroquinone, p-acetamido-                                                                         IV-P                                                       benzoic acid ester                                                        19   2,4-diacetamidophenol                                                                              IV-Q                                                  20   1-acetamido-4-hydroxy-                                                                             IV-R                                                       napthalene                                                                21   1-benzamido-4-hydroxy-                                                                             IV-S                                                       naphthalene                                                               22   1-hydroxy-4-ureido-napthalene                                                                      IV-T                                                  ______________________________________                                    

                  TABLE II                                                         ______________________________________                                         Esters of 16,16-Difluoro-PGE.sub.2                                                                         Product 16,16-                                          Hydroxy Phenol or      Difluoro-PGE.sub.2                                 Ex.  Napthyl Compound       ester of formula:                                  ______________________________________                                         23   p-acetamidophenol      IV-A                                               24   p-benzamidophenol      IV-B                                               25   p-(p-acetamidobenzamido)phenol                                                                        IV-C                                               26   p-(p-benzamidobenzamido)phenol                                                                        IV-D                                               27   p-hydroxyphenylurea    IV-E                                               28   p-phenylphenol         IV-F                                               29   p-tritylphenol         IV-G                                               30   N-acetyltyrosinamide   IV-H                                               31   N-benzoyltyrosinamide  IV-I                                               32   p-hydroxybenzaldehyde semicarbazone                                                                   IV-J                                               33   p-hydroxyacetophenone  IV-K                                               34   p-hydroxybenzamide     IV-L                                               35   N-(p-tritylphenyl)-p-  IV-M                                                    hydroxybenzamide                                                          36   p-hydroxybenzoic acid, IV-N                                                    methyl ester                                                              37   hydroquinone benzoate  IV-O                                               38   hydroquinone, p-acetamido-                                                                            IV-P                                                    benzoic acid ester                                                        39   2,4-diacetamidophenol  IV-Q                                               40   1-acetamido-4-hydroxy- IV-R                                                    naphthalene                                                               41   1-benzamido-4-hydroxy- IV-S                                                    naphthalene                                                               42   1-hydroxy-4-ureido-naphthalene                                                                        IV-T                                               ______________________________________                                    

                  TABLE III                                                        ______________________________________                                         Ester of 16-phenoxy-17,18,19,20-tetranor-PGE.sub.2                                                         Product 16-phen-                                                               oxy-17,18,19,20-                                        Hydroxy Phenyl or      tetranor-PGE.sub.2                                 Ex.  Naphthyl Compound      ester of formula:                                  ______________________________________                                         43   p-acetamidophenol      IV-A                                               44   p-benzamidophenol      IV-B                                               45   p-(p-acetamidobenzamido)phenol                                                                        IV-C                                               46   P-(p-benzamidobenzamido)phenol                                                                        IV-D                                               47   p-hydroxyphenylurea    IV-E                                               48   p-phenylphenol         IV-F                                               49   p-tritylphenol         IV-G                                               50   N-acetyltyrosinamide   IV-H                                               51   N-benzoyltyrosinamide  IV-I                                               52   p-hydroxybenzaldehyde  IV-J                                                    semicarbazone                                                             53   p-hydroxybenzamide     IV-L                                               54   N-(p-tritylphenyl)-p-hydroxybenzamide                                                                 IV-M                                               55   p-hydroxybenzoic acid, methyl ester                                                                   IV-N                                               56   hydroquinone benzoate  IV-O                                               57   hydroquinone, p-acetamidobenzoic                                                                      IV-P                                                    acid ester                                                                58   2,4-diacetamidophenol  IV-Q                                               59   1-acetamido-4-hydroxy-naphthalene                                                                     IV-R                                               60   1-benzamido-4-hydroxynaphthalene                                                                      IV-S                                               61   1-hydroxy-4-ureido-naphthalene                                                                        IV-T                                               ______________________________________                                    

                  TABLE IV                                                         ______________________________________                                         Esters of 17-phenyl-18,19,20-trinor-PGE.sub.2                                                              Product 17-                                                                    phenyl-18,19,20-                                        Hydroxy Phenyl or      trinor-PGE.sub.2                                   Ex.  Naphthyl Compound      ester of formula:                                  ______________________________________                                         62   p-acetamidophenol      IV-A                                               63   p-benzamidophenol      IV-B                                               64   p-(p-acetamidobenzamido)phenol                                                                        IV-C                                               65   p-(p-benzamidobenzamido)phenol                                                                        IV-D                                               66   p-hydroxyphenylurea    IV-E                                               67   p-phenylphenol         IV-F                                               68   p-tritylphenol         IV-G                                               69   N-acetyltyrosinamide   IV-H                                               70   N-benzoyltyrosinamide  IV-I                                               71   p-hydroxybenzaldehyde  IV-J                                                    semicarbazone                                                             72   p-hydroxybenzamide     IV-L                                               73   N-(p-tritylphenyl)-p-hydroxybenzamide                                                                 IV-M                                               74   p-hydroxybenzoic acid, methyl ester                                                                   IV-N                                               75   hydroquinone benzoate  IV-O                                               76   hydroquinone, p-acetamidobenzoic                                                                      IV-P                                                    acid ester                                                                77   2,4-diacetamidophenol  IV-Q                                               78   1-acetamido-4-hydroxy-naphthalene                                                                     IV-R                                               79   1-benzamido-4-hydroxy-naphthalene                                                                     IV-S                                               80   1-hydroxy-4-ureido-naphthalene                                                                        IV-T                                               ______________________________________                                     

I claim:
 1. An optically active compound of the formula ##STR46##or a racemic mixture of that compound and the enantiomer thereof, wherein C_(g) H_(2g) is alkylene of one to 9 carbon atoms, inclusive, in the chain between --CR₁ R₂ -- and terminal methyl; R₁ and R₂ are hydrogen, methyl, ethyl, or fluoro, being the same or different, with the proviso that at least one of R₁ and R₂ is other than hydrogen, and with the further proviso that R₂ is fluoro only when R₁ is hydrogen or fluoro; Y is ##STR47##and E is ##STR48##
 2. The α-semicarbazone-p-tolyl ester of 16,16-dimethyl-PGE₂, a compound according to claim
 1. 3. The N-acetyltyrosinamide ester of 16,16-dimethyl-PGE₂, a compound according to claim
 1. 4. The N-benzoyltyrosinamide ester of 16,16-dimethyl-PGE₂, a compound according to claim
 1. 5. The N-acetyltyrosinamide ester of 16,16-difluoro-PGE₂, a compound according to claim
 1. 6. The N-benzoyltryrosinamide ester of 16,16-difluoro-PGE₂, a compound according to claim
 1. 7. The p-hydroxybenzaldehyde semicarbazone ester of 16,16-difluoro-PGE₂, a compound according to claim
 1. 